I hadn't really considered taking up death metal appreciation as a hobby, but in case I ever did, it's nice to know someone has composed a how-to guide.
Better yet! If you want to shred your vocal cords a la the glamorous George "Corpsegrinder" Fisher of Cannibal Corpse (pictured here), there's a guide to that, too!
This inhaling technique can produce an extreme range of pitch, allowing you to both grunt and squeal like a pig. The incoming airflow will be nowhere near the volume of normal speech. You will need to speak using exaggerated lip movements and the front of the tongue while keeping the back of the tongue muscle in place. While an "inhale vocal tech" may sound "cool", be careful using it. It can (and likely will) damage your vocal cords.
Cool! I mean, gwrrraaaaaahhhhhrrrrrrrhhhhhhaaaaaarrrrr!